My Good Sister Always Pesters Me

Li Yiyang unexpectedly got a "sister" when he was nine years old. She was inseparable from her "sister", but it all ended when her "sister" shattered her beloved relationship. She never saw her "sister" again until six years later, on the day when she was a freshman in high school, she met a girl with creamy skin and a face like a peach blossom. Her heartbeat seemed to have missed a beat... "Yes, sister?"